1. Field of the Invention
The present invention relates to an image forming apparatus which transfers a toner image placed on an image carrier onto a recording material using a technology of an electrophotographic apparatus such as a copier or a laser printer. Specifically, the present invention relates to an image forming apparatus which includes a transfer belt for transferring and conveying a recording material.
2. Description of the Related Art
In an electrophotographic apparatus which carries and conveys a recording material using a transfer belt suspended by a plurality of suspension members, there is a configuration using a method of forming a patch image for adjustment on the image carrier to achieve a high quality. However, when the patch image passes through a transfer unit that transfers a toner image from the image carrier onto the recording material, the patch image separates from the image carrier and attaches to the transfer belt. To remove the patch image attached to the transfer belt, it is preferable to bring a cleaning blade into contact with the transfer belt. However, continuous contact of the blade with the transfer belt impairs the durability of the transfer belt. Therefore, to remove the patch image while reducing damage to the durability of the transfer belt, there is a method in which the blade stays away from the transfer belt in a standby state and comes into contact with the transfer belt when the patch image is to be removed.
However, if a contact position at which the blade comes into contact with the transfer belt is away from the transfer unit on the downstream side of the transfer unit, the transfer belt has to move a long distance the toner, which is transferred from the image carrier and attached onto the outer peripheral surface of the transfer belt in the transfer unit. To reduce the moving distance of the toner, the blade preferably contacts the transfer belt at a location where a separation suspension roller suspends the transfer belt.
In the configuration in which a recording material is transferred in an electrostatic manner, the recording material is attracted to the belt during a transfer operation. Accordingly, a separation suspension roller is used to separate the recording material from the belt when the recording material is attracted to the belt.
However, as the types of paper increase, it is difficult to handle this issue only by the separation suspension roller. In other words, particularly it is difficult to separate a recording material when the recording material has a weak stiffness. To solve this problem, Japanese Patent Application Laid-Open No. 5-341664 discusses the configuration in which a roller is provided as a push-up unit capable of moving a transfer sheet between a push-up position and a non-push-up position from the inner side thereof. In this configuration, a recording material is separated in such a manner that a push-up roller pushes up the transfer sheet. On the other hand the transfer sheet is not pushed up while a recording material does not need to be separated.
In a case where such a configuration is applied to a transfer belt, a push-up unit, which locally pushes up the transfer belt during a separation process, is disposed on the upstream side or the downstream side of the separation suspension roller in a conveying direction of a recording material. In the case of using a recording material having a weak stiffness such as a thin paper sheet, the recording material is conveyed in a state where the transfer belt is locally pushed up so that waviness occurs in the recording material, which increases the stiffness of the recording material during the separation process. However, if the push-up unit is disposed on the downstream side from the separation suspension roller, the conveying direction of the separated recording material when the separation suspension roller is used, becomes considerably different from the conveying direction of the separated recording material when the push-up unit is used. In order to reduce the difference in the conveying direction of the separated recording material, the push-up unit is disposed on the upstream side of the separation suspension roller. However, the separation position of the recording material, in a case where the push-up unit is used, is away from the separation suspension roller to the upstream side of the separation suspension roller in the conveying direction of the recording material. As a result, a distance between a guide member which guides the separated recording material and the separation position increases, which is likely to cause a conveying error between the recording material and the guide member. For such a case, in order to suppress the conveying error between the recording material and the guide member, the distance between the separation position and the guide member should not be too long. Therefore, the push-up unit is configured to be disposed near the separation suspension roller.
A patch image for adjustment may be formed sometimes on an image carrier subsequently to a toner image to be transferred onto a recording material that is separated by the push-up unit. The patch image on the image carrier is attached to the transfer belt in the transfer unit.
However, since the blade contact position where the blade for removing the patch image comes into contact with the transfer belt is provided at the separation suspension roller, the blade and the push-up unit are disposed to be adjacent to each other. If the timing in which the blade for removing the patch image comes into contact with the transfer belt is set to be prior to the timing in which the push-up unit retreats from the transfer belt, the contact surface of the blade is affected by a push-up operation so as to wave in the width direction. As a result, the contact of the blade becomes unstable.